So many young people today get incorrect facts about how sex really works, because of taboos built into our culture. As long as schools aren't teaching what is right or wrong and merely present the facts, I think its a tremendous service. Parents should be the one's in many cases to have the first talk about the bird and bees, but schools should reinforce this with fact since some religions don't even give the basics.
Students who are going through puberty should learn about what is happening to them. It's important that they learn from trained teachers, or they might turn to the Internet or TV, which can give them an unrealistic impression of what sex it actually like. Kids need to learn how to be safe and healthy.
Kids have to learn about sex from somewhere, and I would rather it be in the classroom than in the streets or on TV. Unfortunately, the hundred mile wide puritanical streak that runs our society means that kids often learn about the birds and the bees from anyone, anywhere but from an educator in a classroom setting. The result? Skyrocketing rates of teenage pregnancies, abortions, sexually transmitted diseases. We can't pretend that kids aren't having sex, because the consequences are all to readily apparent. Let's make it safer, please.